Presently known ultrasound visible instruments include that disclosed in WO 98/18387 which provides a probe insertable into a material containing a liquid and having a coating comprising a carrier material and a quantity of reactive material which, upon contacting a reactant, produces a quantity of bubbles adjacent the coating for reflecting ultrasonic energy. In the particular application, the probe comprises a biopsy needle and the coating is positioned towards a sharp distal end thereof, thereby to facilitate the guidance and positioning thereof. Alternatively the coating can be provided along the entire length of the instrument or at discrete portions along its length. The reactive material comprises, for example, a mixture of sodium hydrogen carbonate and citric powder contained within a single layer of a carrier material which facilitates interaction between an externally supplied fluid and the reactant. In operation, the fluid permeates through the carrier material and, once the two reactive components are wetted thereby a reaction takes places which produces a plurality of bubbles which are mobile within the carrier material in a manner which enhances the ultrasound reflectivity of such of a device over and above that presently known from similar devices.